The advantages of a saw blade or band having extremely hard cutting teeth and a tough, fatigue-resistant backing body have been known and understood for many years. Quite early in the art a compound or laminated steel strip consisting of a narrow band of very hard steel welded to one edge of a wide band of softer steel was employed for this purpose, the teeth being in the hard steel band. U.S. Pat. No. 1,521,857 to Blum is an example of this technique.
Another approach to producing hard cutting teeth on a fatigue-resistant saw blade is through selective heat treatment and tempering of the blade, i.e. giving the teeth a heat treatment different from that of the rest of the blade. This technique forms the basis for U.S. Pat. No. 1,130,649 to Whitaker and U.S. Pat. No. 1,352,140 to Napier.
A third approach to saw construction consists in brazing or similarly fastening hard steel or carbide inserts or tips in or to the saw teeth. Examples of this technique are found in U.S. Pat. No. 2,318,549 to Wilkie and U.S. Pat. No. 2,880,768 to Kolesh.
The success of a saw blade made by this third technique, that is, having hard steel or carbide inserts fastened thereto, depends on the security of the fastening and the support given the cutting tips by the body of the teeth. The above-noted patent to Kolesh recognized this requirement and in an attempt to meet it swaged the leading face of the saw teeth to provide seats of increased area to support the hard metal or carbide tips which were brazed or similarly anchored thereto. This technique, however, was criticized in a subsequent U.S. Pat. No. 3,034,378 to Anderson because of the difficultly of handling the small carbide tips.
Anderson also criticized Kolesh because of the nature of the brazing technique used to secure the carbide tips to the steel. Brazing materials customarily used are non-ferrous, brass being the most common. These materials may become brittle, especially where the area of the bond is small in relation to the effective cutting edge of the tool, as is the case in a saw blade. Furthermore, the temperatures reached by a carbide tip during a cutting operation can sometimes exceed the melting point of the brazing material.
In U.S. Pat. No. 3,034,378, Anderson proposed a method for fusing a carbide tip to a steel saw blade by an electric-welding technique. The carbide of which the tip is formed is provided in a rod-like configuration, up to several feet in length, preferably having a rectangular cross section. During the welding operation, the portion of the tooth continguous to the rod becomes heated to its fusion temperature and hence softens, but the carbide rod retains its form. Pressure exerted on the rod then forces the rod into the adjacent portion of the tooth as the weld is formed. After the tip is welded, the junction is annealed to relieve stresses in the steel. After these operations are completed, a diamond cutting wheel severs the carbide fused into the tooth from the remainder of the carbide rod, readying the carbide rod for the next cyclical operation. The discrete carbide tips which Anderson found unwieldy in Kolesh were thus eliminated.
In U.S. Pat. No. 3,295,396 to Kolb, a resistance welding process and apparatus for welding a tip on a saw tooth is disclosed. In such technique, the tip material is again separated from a welding rod after the welding process. The saw is annealed after the welded tip has been shaped by grinding.
U.S. Pat. No. 4,205,564, also to Kolb, discloses use of discrete, rectangular tips carried on a foil tape to each tooth. A tip and its underlying foil tape are pressed against the tooth while the tooth is heated using a torch or resistance welding technique. Preferably, the foil tape carrier for each tip is made of a brazing material so that the resulting joinder of tip and tooth is by a combination of brazing and welding.
U.S. Pat. No. 3,800,633 to Funakubo discloses a method for forming tungsten-carbide tipped saw blades. The Funakubo saw is first preprocessed to cut a notch in each tooth for receiving the tip. A preformed tip is then inserted into the notch and brazed in place.
U.S. Pat. No. 4,462,293 to Gunzner discloses a method for tipping saw teeth with carbide-containing steel. Like the Funakubo method, the saw must first be ground to provide notches in the teeth into which the carbide-containing tips are to be welded.
U.S. Pat. No. 2,683,923 to Replogle discloses a method for fusion welding tips to saw blades. The Replogle technique relies on three distinct zones of metal, a first zone being the cutting edge, the third zone being the base material and the intermediate zone being provided principally by a welding rod or wire and having a composition intermediate the composition of the first and third zones.
In recent years, Stellite has become a popular material for tipping saw blades. Stellite is a class of hard, wear and corrosion-resistant non-ferrous alloys composed principally of cobalt (20-65 percent), together with lesser amounts of chromium (11-32 percent) and tungsten (2-18 percent) that exhibits exceptionally high resistance to softening at high temperatures.
An example of an apparatus adapted to apply Stellite tips to saws is the ISELI tipping machine, distributed in the United States by H.S. International, Inc. and in Canada by Chaston Industrial Saw, Ltd. The ISELI machine employs Stellite in extruded rod form which is cut by the machine into short lengths and then resistance welded to the tooth of a saw blade. After the tooth has been tipped with Stellite, it is advanced to an adjacent station at which the weld is annealed by an electric element. This process is repeated until all teeth have been processed at both the welding and annealing stations.
One of the problems of the ISELI machine is that approximately fifty percent of the Stellite material is wasted, being ground away during the grinding operation. Furthermore, the grinding operation is unduly time consuming due to the substantial amount of material that must be removed.
Vollmer Werke Maschinenfabrik GmbH of West Germany markets Stellite tipping machines under the designations GF10U and GWA11U. The GF10U is a manual machine that relies on a skilled operator to apply material from a Stellite welding rod to the tooth using a welding torch. Saw teeth tipped by the GF10U machine are desirably preprocessed by swaging or cutting to provide a larger surface area for Stellite application.
The GWA11U machine is similar to the GF10U, but employs automated handling of the Stellite welding rod and the welding torch. The welding torch is ignited in intervals, depending on the particular cycle selected, and the molten Stellite drops onto the blade. Annealing is accomplished by a welding torch placed subsequently to the welding point.
The GWA11U machines suffer by use of a welding torch for the delicate annealing operation. It is very difficult to control the annealing parameters when using a gas or plasma torch operating at 6000 degrees.
ETS Alligator of Paris, France, markets a tipping machine under the designation Depomatic Plasma PS that employs a plasma torch to weld Stellite rod to the tips of saw blades. One version of the machine uses the same plasma torch to anneal all of the tips after all of the welding operations are completed. The second version uses an induction heating coil.
The gas plasma and TIG welding techniques employed in these prior art machines are necessarily complex, requiring carefully tailored starting and extinguishing cycles in which the start voltage, start ramp, high voltage start, ramping parameters, gas mix, wire feeding rate, et cetera, must all be set.
From the foregoing it will be recognized that all of the prior art techniques suffer from a variety of drawbacks which make them poorly suited for the simple, reliable and economical application of tipping material, particularly Stellite, to saw blades and the like.
Accordingly, it is a principal object of the present invention to provide a method and apparatus for tipping saw blades that overcomes these drawbacks found in the prior art.
Another object of the present invention is to provide a method and apparatus for providing Stellite tips to a saw blade by techniques which are faster, more effective and more consistent than prior art techniques.
Yet another object of the present invention is to provide a method and apparatus for applying tips to saw blades, which tips are adapted for ease of manipulation and orientation by an automatic tipping machine.
Still another object of the present invention is to control the period during which welding heat is applied to a tip/blade junction by monitoring the displacement of the tip into the blade.
According to the present invention, wear-resistant tips, preferably comprising preformed pellets of Stellite in square configuration, are welded, cooled and subsequently annealed to a saw tooth at a single machine station in rapid succession. A head assembly manipulates the individual pellets and positions them properly on the saw blade for forging thereto. The square configuration of the pellets permits their reliable manipulation and orientation by the automated equipment. The duration of the pellet welding phase is determined by the displacement of the pellet into the saw blade, rather than by reliance on a predetermined time period. After cooling, the annealing is accomplished by using the same electrical power supply as is employed for the welding. The duty cycle of this power supply, however, is regulated to produce the amount of annealing heat required for the particular steel being worked. After the welding, cooling and annealing operations are performed on one saw tooth, the saw is indexed to bring the next tooth into position for processing.
The foregoing and other objects, features and advantages of the present invention will be more readily apparent from the following detailed description of a preferred embodiment thereof, which proceeds with reference to the accompanying drawings